Environmental Science Graduate Program, The Ohio State University, Columbus, OH, USA.
Microb Biotechnol. 2014 Jul;7(4):332-46. doi: 10.1111/1751-7915.12125. Epub 2014 Apr 1.
Mixed plug-flow loop reactor (MPFLR) has been widely adopted by the US dairy farms to convert cattle manure to biogas. However, the microbiome in MPFLR digesters remains unexplored. In this study, the microbiome in a MPFLR digester operated on a mega-dairy farm was examined thrice over a 2 month period. Within 23 days of retention time, 55-70% of total manure solid was digested. Except for a few minor volatile fatty acids (VFAs), total VFA concentration and pH remained similar along the course of the digester and over time. Metagenomic analysis showed that although with some temporal variations, the bacterial community was rather stable spatially in the digester. The methanogenic community was also stable both spatially and temporally in the digester. Among methanogens, genus Methanosaeta dominated in the digester. Quantitative polymerase chain reaction (qPCR) analysis and metagenomic analysis yielded different relative abundance of individual genera of methanogens, especially for Methanobacterium, which was predominant based on qPCR analysis but undetectable by metagenomics. Collectively, the results showed that only small microbial and chemical gradients existed within the digester, and the digestion process occurred similarly throughout the MPFLR digester. The findings of this study may help improve the operation and design of this type of manure digesters.
混合推流式环型反应器（MPFLR）已被美国许多奶牛场广泛采用，用于将牛粪转化为沼气。然而，MPFLR 消化器中的微生物组仍未得到探索。本研究在两个月的时间内对大型奶牛场的 MPFLR 消化器中的微生物组进行了三次检查。在 23 天的停留时间内，55-70%的总粪便固体被消化。除了少数少量的挥发性脂肪酸（VFAs）外，总 VFA 浓度和 pH 值在消化器的整个过程中和随时间推移保持相似。宏基因组分析表明，尽管存在一些时间变化，但细菌群落在消化器中的空间上相对稳定。消化器中的产甲烷群落也在空间和时间上保持稳定。在产甲烷菌中，Methanosaeta 属占主导地位。定量聚合酶链反应（qPCR）分析和宏基因组分析得出了产甲烷菌个别属的相对丰度不同，特别是 Methanobacterium，根据 qPCR 分析，它是优势菌属，但在宏基因组学中无法检测到。总的来说，结果表明消化器内仅存在较小的微生物和化学梯度，并且消化过程在整个 MPFLR 消化器中相似。本研究的结果可能有助于改进这种类型的粪便消化器的运行和设计。
